#weight = float(input("Please input weight of your cargo:"))
#if weight <= 20:
#    print('For free\n')
#elif weight <= 30:
#    print('The price is', (weight-20)*5, 'yuan\n')
#elif weight <= 40:
#    print('The price is', (weight-30)*10+50, 'yuan\n')
#elif weight <= 50:
#    print('The price is', (weight-40)*15+150, 'yuan\n')
#else:
#    print('More than 50kg, no permission\n')


#for cock in range(0, 20):
#    for hen in range(0, 33):
#        chick = 100-cock-hen
#        if chick%3==0 and cock+hen+chick==100 and cock*5+hen*3+chick/3==100:
#            print('cock=', cock, ' hen=', hen, ' chick=', chick, '\n')

#i=2
#while i<=100:
#    flag=0
#    for j in range(2, i-1):
#        if i%j==0:
#            flag = 1
#            break
#    if flag==0:
#        print(i,end=' ')
#    i+=1
#print('')

#while True:
#    size = int(input("input size="))
#    for i in range(size):
#        for j in range(size-i-1):
#            print(end=' ')
#        for j in range(2*i+1):
#            print(end='*')
#        print('')


#info = {'吕红':'数据库', '肖扬':'Python', '丁锦':'英语', '周婷':'线性代数', '李娟':'数据库', '周玲玲':'Java'}
#info['赵红'] = 'Java'
#info['周玲玲'] = 'Python'
#del info['周婷']
#for item in info.items():
#    print(item)

#secret = {'张三':'abcde', '李四':'qwert', '王五':'12345'}
#flag = 0
#user = input('请输入用户名:')
#for count in range(0, 3):
#    passwd = input('请输入密码')
#    if secret[user] == passwd:
#        flag = 1
#        break
#    else:
#        print('密码不正确，请重新输入')
#        print('')
#if flag == 1:
#    print("密码正确，登录成功")
#else:
#    print('输入超过三次，退出登录')
#

str1 = input()
set1 = set(str1)
list1 = list(set1)
list1.sort(reverse=False)
list1 = "".join(list1)
print(list1)
